Recently, display devices using liquid crystal (hereinafter, referred to as display) are spreading at conspicuous pace. The display of this type is low in power consumption and improved in saving space in comparison with a CRT display. Accordingly, it is important to make use of the merits of such a display and produce a display that is lower in power consumption and improved in saving space.
FIG. 11 is a block diagram of a system to implement display through a display device with a TFT display. This system is constituted with an image signal source 100 and a TFT liquid crystal display panel 101. The image signal source 100 is formed, at least, by a CPU 100A, a RAM 100B, a frame memory 100C and an LCD controller 100D. The CPU 100A is operation control means to transmit display data while exchanging data with the RAM 100B as a general-purpose memory. This memory RAM 100B is not especially provided only as a display memory, and hence requires newly a memory to store data for display. It is the frame memory 100C. The frame memory 100C. temporarily stores display data for one screen of a liquid crystal panel 101C (hereinafter, the data for one pixel is given as display data, and each binary signal forming the display data is referred to as an image signal). The LCD controller 100D is to implement transmission control or the like of display data, in order to display in timing the display data stored in the frame memory 100C in display positions on the liquid crystal panel 101C. Herein, although for the CRT there is a need to transmit the display data through conversion into analog data, the display data herein is transmitted by an image signal as digital data on the assumption that the interface of the liquid crystal display corresponds to digital data. If the image signal is digital data, D/A conversion is not required on the side of the TFT liquid crystal display panel 101.
Meanwhile, the TFT liquid crystal display panel 101 is structured with a scanning line driver 101A, a digital data driver 101B and a liquid crystal panel 101C. The scanning line driver 101A controls display in a scanning line (row) direction on the basis of timing data transmitted from the LCD controller 100D. The digital data driver 101B can receive and process digital-data image signal. The digital data driver 101B controls display in a data-line (column) direction on the basis of timing data transmitted from the LCD controller 100D. Thereupon, display tonal level is also controlled. The liquid crystal panel 100C is a panel having TFTs (Thin Film Transistors) to make display under the control of the scanning line driver 01A and digital data driver 101B.
In such a system, the LCD controller 100D must transmit to the digital data driver 101B the display-data image signal for the entire screen temporarily stored in the frame memory 100C. Moreover, transmission timing by progressive scanning is fixed. Consequently, there is a need to transmit image signals in timing also for the display data on the pixels not requiring display change. Due to this, there is an increase in useless data transmission amount and hence increase in power consumption. Thus, reduction of power consumption cannot be achieved.
Therefore, it is an object of the present invention to obtain a display device of a space-saved design having a structure for achieving consumption-power reduction and moreover taking into consideration layout efficiency particularly for the case of integrally forming the peripheral circuit over a glass substrate.